Number of 3-step knight's tours on an (n+2) X (n+2) board summed over all starting positions.

Terms

a(0) =16a(1) =104a(2) =328a(3) =664a(4) =1112a(5) =1672a(6) =2344a(7) =3128a(8) =4024a(9) =5032a(10) =6152a(11) =7384a(12) =8728a(13) =10184a(14) =11752a(15) =13432a(16) =15224a(17) =17128a(18) =19144a(19) =21272a(20) =23512a(21) =25864a(22) =28328a(23) =30904a(24) =33592a(25) =36392a(26) =39304a(27) =42328a(28) =45464a(29) =48712